The present invention relates to a heat transfer apparatus and a method for controlling the transfer of heat from a roof space into a living space of a building and relates particularly, though not exclusively, to a heat transfer system that can also be employed to cool the living space.
It is generally known that the temperature of air trapped in a roof space, that is, the air held in the void between the roof cladding material and the ceiling of a building, is considerably higher than the ambient air temperature. The trapped air in the roof space becomes heated due to thermal energy from sunlight which is conducted through the roof tiles or other roof cladding material and re-radiated into the roof space. Some heating may also occur due to heat conducted through the ceiling from the living space below. The degree of heating of the air in the roof space to elevated temperatures is determined by a number of factors, including the amount (intensity and duration) of sunlight that the roof is exposed to, the ambient (outside) air temperature and the extent of roof insulation.
Several prior art systems attempt to exploit the heat accumulated in the roof space for heating a living space below. For example, AU-B-32409/84 discloses a Ventilator which can be used for recycling heated air from a roof cavity of a building or like structure back into a living/work area of the structure. The ventilator assembly of AU-B-32409/84 may be sited in either the roof or ceiling of the structure, and has an axial flow fan for generating a flow of heated air through the assembly. A temperature sensing means 8, for example, a thermostat, may be provided to switch the fan on or off as required. The temperature sensing means 8 may be located within the ventilator assembly or positioned remote from the assembly with interconnecting wiring. AU-A33942/93 discloses a ventilation system designed specifically for ventilating warm air from a roof space for heating a living space below. The system of AU-A33942/93 includes a vent 12 mounted in the ceiling 14 of a house and opening into the living space below, and a ducting means 18 in the form of a concertina ducting tube located in the roof space to provide communication of air from a high point within the roof space to the vent 12. An electric fan 20 forces air to flow through the ducting tube 18 and vent 12 so that warm air can be ducted from the roof space into the living space. The system of AU-A-33942/93 may include a thermostatically controlled switching circuit adapted to switch automatically between summer and winter modes in response to changes in the ambient (exterior) air temperature. The electric fan is solar powered.
One of the disadvantages of these prior art systems is that they do not provide any adequate means for controlling the transfer of air from the roof space at a sufficiently elevated temperature to ensure heating of the living space below. The present invention was developed with a view to providing a heat transfer system that can ensure air is only transferred from the roof space when the temperature of the air in the roof space exceeds the temperature of the air in the living space by a predetermined amount.
Throughout this specification the term xe2x80x9ccomprisingxe2x80x9d is used inclusively, in the sense that there may be other features and/or steps included in the invention not expressly defined or comprehended in the features or steps subsequently defined or described. What such other features and/or steps may include will be apparent from the specification read as a whole.
According to one aspect of the present invention there is provided a heat transfer apparatus for heating a living space in a building, the apparatus comprising:
air transfer means arranged within a roof space of the building for transferring warm air from within the roof space into a living space below;
an electric fan arranged to force air through said air transfer means into the living space;
a first temperature sensor within the roof space for sensing a first air temperature within the roof space;
a second temperature sensor within the living space for sensing a second air temperature within the living space; and
an electronic controller operatively connected to said electric fan and said first and second temperature sensors, and wherein said controller ensures that the electric fan is only activated when the first air temperature exceeds the second air temperature by a first predetermined temperature difference and when the first air temperature exceeds a predetermined threshold temperature whereby, in use, warm air transferred from the roof space is able to heat the living space.
More preferably the electric fan is only activated when the second air temperature is below said preset room temperature by a second predetermined temperature difference. Advantageously said preset room temperature is adjustable by an occupant of the living space.
Preferably said controller also ensures that the electric fan is only activated when the first air temperature exceeds a predetermined threshold temperature. More preferably the electric fan is only activated when the first air temperature exceeds the predetermined threshold temperature by a third predetermined temperature difference. Typically said predetermined threshold temperature is set at between 20xc2x0 C. and 25xc2x0 C. More typically the predetermined threshold temperature is set at approximately 22.75xc2x0 C.
According to another aspect of the present invention there is provided a method for controlling the transfer of heat from a roof space into a living space of a building using an electric fan to force warm air from the roof space of the building into the living space below, the method comprising:
sensing a first air temperature within the roof space;
sensing a second air temperature within the living space; and
activating said electric fan only when the first air temperature exceeds the second air temperature by a first predetermined temperature difference and when the first air temperature exceeds a predetermined threshold temperature whereby, in use, warm air transferred from the roof space is able to heat the living space.